One of the processes for manufacturing mineral fibers is the flame attenuation process. This is typically employed to manufacture glass fibers by first forming glass marbles or pellets in a conventional glass furnace, then at a later time remelting the marbles or pellets in a crucible containing a large number of small orifices. Glass issuing from the crucible orifices is initially attenuated by a mechanical pull-roll assembly which pulls the molten glass into the form of small diameter glass rods, known as primary filaments or "primaries". The primaries are then further attenuated by a hot high velocity jet of combustion gases emitted from a burner to form fine glass fibers.
A pull-roll assembly basically comprises a drive roll mounted in a stationary support and an idler or driven roll mounted in a movable support. The idler roll is biased against the drive roll by a spring arrangement to cause the drive roll to rotate the idler roll. The movable support that carries the idler roll is locked in place so that constant pressure is applied to the idler roll. A conventional type of locking mechanism comprises an assembly consisting of two latch arms located at opposite ends of the pull rolls. Each latch arm is pivotally mounted on the movable idler roll support and has a hooked end which engages a latch pin on the stationary support. The latch arm is typically biased into locking position by a leaf spring which engages both the latch arm and the movable idler roll support. Such an arrangement is described in more detail in U.S. Pat. No. 4,414,010, which issued on Nov. 8, 1983 in the name of Chin et al.
Although the fiber forming operation is continuous, the pull-roll assemblies have to be monitored by operators who from time to time are required to clear the pull rolls of foreign objects or replace one or both of the rollers. This requires the operator to press a release bar connecting the latch arms with enough force so as to move the latch arms against the tension of the springs and out of engagement with the latch pins. As shown in FIG. 1 of the aforementioned patent, which illustrates a typical arrangement of this type, this would require the release bar 106 to be pushed against the force of the leaf springs 112 in order to unlatch the latch arm hooks 108 from the latch pins 110. Although the drawing in the patent is on a small scale, it can be seen that the latch hook extends around a considerable portion of the circumference of the pin 110 in order to prevent the hook from becoming disengaged. To release the hook from the pin it is therefore not enough to simply press down on the release bar since this would merely cause the portion of the hook beneath the pin to be lifted up against the pin. To actually remove the hook from the pin it is necessary to also push the release bar toward the drive roller an amount to allow the hook to clear the pin. This is difficult to do, although possible, when the rolls are in face-to-face contact because the rubber covering on the pull rolls can be compressed to an extent. It is very difficult to accomplish, however, when a foreign object is in the nip of the rolls, as the movable support has to be moved still an additional amount corresponding to the thickness of the object.
In actual practice the extent of the contact between the hook and the pin can be substantially greater than as shown in the patent. Thus in actual practice, if the finger or hand of an operator should get caught between the rolls it would be extremely difficult to unlatch the mechanism simply by exerting force on the release bar.
It is therefore an object of the invention to provide a pull roll latching mechanism which allows the latch to be released simply by pressing on the release bar with a medium amount of pressure, even with a thick foreign object in the nip of the rolls. The latching mechanism of such an arrangement must, however, be able to maintain the movable roll support in operative position against the forces of vibration and other stresses of operation which tend to move the latch out of locked condition.